• Energy Research

The constant operation of water electrolyzers prevents degradation caused by operational fluctuations, preserving performance. This study introduces a MILP-based design framework for hybrid energy storage systems, integrating photovoltaic systems, Lithium-ion batteries, and alkaline electrolyzers operating at constant rated conditions. The framework targets energy-independent residential users, fully meeting electrical loads while incorporating spatial analysis via a GIS-based management module. Applied to the Italian context, the framework uses historical data for residential end-users with 1.5−3.0 kW electrical loads. The results indicate photovoltaic systems sized between 3.0−4.5 kW, Lithium-ion batteries with 6.0−7.0 kWh capacity, and alkaline electrolyzers sized at 100−260 W for daily loads of 2.8−6.0 kWh. Lithium-ion batteries account for approximately 60 % of the total system cost. A levelized hydrogen cost of 12−19 €/kg is required to cover the overall investment costs. Additionally, the system offers environmental benefits, with CO 2 emission reductions of approximately 0.35 to 0.83 tons per user annually.

Abstract Energy efficiency interventions in Water Supply Systems (WSSs) need a precise evaluation of the available water flow rates for energy recovery interventions; however, flow meters are generally too costly for being installed in all the gravity adduction pipelines of a WSS. This paper presents a methodology for predicting flow rates in gravity adduction pipelines based on the electricity bill consumption. In this study, the predicted average flow rate is 0.0300 m3∗s−1, being 1.64% lower than the real one. A Pelton turbine has been chosen as energy recovery unit for supplying electricity to a pumping station of a preloading tank where the water is treated to make it drinkable. An energy saving of 475.26 (MW∗h)∗year−1 is achieved, which can be also expressed as 88.87 saved Tonnes of Oil Equivalent (TOE) and 204.36 ktCO2 not released into the atmosphere. The gross economic saving due to the installation of the Pelton turbine is equal to 94.29 k€∗year−1 and it can be further increased up to 116.51 k€∗year−1 if the energy efficiency certificates issued by the Italian Authorities are considered. The Payback Period (PBP) of the intervention corresponds to 3 years, and a Net Present Value (NPV) after twenty years is approximately 1.4 M€.

The overuse of fossil fuels has brought considerable climate change to our planet, affecting not only human life, but also the ecosystem of the Earth (e [...]

Abstract Among the most used hydraulic machines in the small-scale hydropower sector, Pump-as-Turbine (PaT) technology is suitable for both practical and economical aspects. These machines are already profitably applied in remote and rural zones for electricity production and in energy recovery applications in both civil and industrial plants, like Water Distribution Networks (WDNs) and chemical plants. Several studies aimed to provide theoretical formulas able to forecast flow rate and head at the Best Efficiency Point (BEP) in turbine mode obtaining, however, contrasting results and a lack of generalization. In this work, a generalized theoretical methodology for forecasting the flow rate, the head and the efficiency of PaTs at their BEP is studied. Specific correlations between the non-dimensional parameters of PaTs in pump and in turbine mode are presented and discussed. The accuracy of the presented methodology is compared to the ones available in literature showing a good generalization capability and a significant improvement in forecasting the behaviour of the PaT, starting from the available performance characteristics in pump mode.

Abstract Waste Heat Recovery (WHR) from energy intensive industries has a great potential in curbing CO2 emissions. Among the different solutions, District Heating (DH) is considered of major interest, satisfying the heating demand of users in the proximity of power plants. Considering the energy intensity of the pulp and paper industry, a method for evaluating the recovery potential of its low-grade waste heat from cogeneration plants in DH is presented. The proposed method allows to evaluate the thermal power from cogeneration plants to end users and to assess the potential maximum number of residential buildings that could be connected to each DH network. Based on the proposed method, the benefits of the WHR are evaluated from both energy and environmental points of view. More precisely, considering 50 pulp and paper mills in Italy under investigation in the present analysis, a yearly natural gas saving corresponding to 143.76 kTonnes of Oil Equivalent (TOE) and 333.11 ktCO2 is obtained. In case of WHR, the average Primary Energy Saving (PES) of the cogeneration plants increases from 0.14 up to 0.22. In particular, cogeneration units based on steam turbine technology show the greatest improvement, since its average PES moved from 0 up to almost 0.1.

Abstract Energy recovery solutions reduce considerably the carbon footprint of Water Supply Systems (WSSs), which accounts for a large share of the energy demand in urban areas. The evaluation of the potential saving requires the availability of water flow rate and net head values in WSSs pipelines; however, this task is not always achievable since flow meters are costly and not installed in all the pipelines. In this paper, a novel methodology to predict the yearly average flow rate in gravity adduction pipelines is presented and validated using measured data coming from a WSS in Italy. A methodology already developed by some of the authors of this work was used to select Pump-as-Turbines (PaTs) and evaluate their Best Efficiency Point (BEP) to maximize the energy recovery. Two different installation layouts were investigated, namely one PaT and two PaTs in parallel, to be installed in the selected branches. The first one showed the best economic profitability, leading to a saving of 1325 €/year and a PayBack Period (PBP) of 11 years. The branch with the highest energy recovery potential led to a saving of 4915 €/year and a PBP of 6 years. Energy Efficiency Certificates (ECCs) were considered, highlighting their pivotal role to lower PBPs.

When axial flow pumps-as-turbines (PATs) operate under off-design conditions, unstable and unsteady flow structures appear in the internal flow field, resulting in suboptimal functioning. These operating conditions not only decrease the efficiency of the hydraulic machines but also affect their mechanical reliability. This study establishes relative streamline coordinates, based on the blade's mean camber line, to investigate flow instabilities in axial flow PATs from a new perspective. Numerical simulations on an axial flow PAT were performed and validated using experimental data. The results show that flow separation is more likely to occur due to the more curved profile at the blade's suction surface, leading to considerable fluctuations in velocity along the flow direction and enstrophy amplitude near both the hub and impeller shroud. Moreover, the poor matching of the relative inflow angle of the impeller with the blade inlet angle leads to impingement losses near their leading edge, generating unstable flows and significant pressure pulsations, which induces hydraulic instability within the impeller. In addition to rotor-stator interference effects, the curvature of the blade suction surface profile and the bend structure of inlet conduit are significant factors that influence the pressure pulsation distribution of the PAT. An analysis of the enstrophy transport equation indicates that the relative vortex generation and the Reynolds stress dissipation terms play a key role in both vortex generation and dissipation, whereas the viscous term has a lower influence. These findings can serve as a reference for the optimization and efficient design of axial flow PATs.

Technologies capable of efficiently exploiting unavoidable CO2 streams, have to be deeply investigated and deployed during the transition phase to achieve long-term climate neutrality targets. Among the technologies, Molten Carbonate Cells (MCC) Operating in Electrolysis Mode (MCEC) represents a promising facility to valorize CO2-rich waste streams, which are typically available in industrial plants, by their conversion into a high-value H2/CO syngas. These gaseous products can be reintegrated in a plant or reused in different applications. This study analyzes the integration of a system of the MCEC unit under different operating conditions in terms of composition, current density, and the utilization of fuels in a steam-reforming process of an Italian oil refinery via a mixed experimental-simulative approach. The aim of the current study is to assess the improvement in the overall product yield and further impacts of the MCEC unit on the plant efficiency. The results have shown that it is possible to obtain an electrochemical Specific Energy Consumption for the production of H2 of 3.24 kWh/NmH23 using the MCEC, whereby the possible integration of a 1-MWe module with a reformer of the proposed plant not only increases the hydrogen yield but also decreases the amount of fuel needed to assist the reforming reaction and separates a CO2 stream after additional purification via an oxy-fuel combustor, consequently determining lower greenhouse gases emissions.